Adaptive Planar Chirality of Pillar[5]arenes Invertible by -Alkane Lengths.

Chirality of host molecules can be induced and/or inverted by the guest molecules. However, the adapting chirality of hosts to the length of -alkanes remains a great challenge because -alkanes are neutral, achiral, and linear molecules, resulting in a weak interaction with most compounds. Herein, we report a system with chirality adapted to -alkane lengths, using a pillar[5]arene-based macrocyclic host, , which contains five stereogenic carbons and five terminal bromine atoms on each rim. The electron-rich cavity of could include -alkanes and the planar-chiral isomers sensitively inverted in response to the lengths of the complexed -alkanes. The inclusion of a short -alkane such as -pentane made more inclined to be in the -form, whereas the inclusion of long -alkanes such as -heptane made the -form more favorable. The difference in the stability of the isomers was supported by the crystal structures and the theoretical calculations. Furthermore, temperature drives the adaptive chirality of with -alkanes. An -alkane with middle length, -hexane, showed the dominance of the -form of at a higher temperature, whereas the -form was shown at a lower temperature.